1. Field of the Invention
The present invention relates to an elastic member for an ink-jet recording apparatus, an ink tank and an ink-jet recording apparatus. More particularly, the present invention pertains to an elastic member which is used as an ink tank valve, a sealing member for an ink tank, and the like items in an ink tank to be employed in an ink-jet recording apparatus that records printed letters on a recording medium by supplying a recording head with an ink, and is also used as a sealing member for preventing an ink from leaking through a recording head in the main body of an ink-jet recording apparatus; which can be injection molded by two-color molding method; and which is composed of a material excellent in durability. The present invention relates also to an ink tank using said elastic member; and further to an ink-jet recording apparatus using the same.
2. Description of the Related Arts
An ink-jet recording apparatus has heretofore been equipped with an ink tank which has an ink chamber to be filled in with an ink and an ink supply portion that supplies a recording head portion with an ink. Examples of types of the ink tanks include a type which is constituted so that an ink is supplied to a recording head which is stationarily attached to a carriage, through tubes arranged everywhere in an ink-jet recording apparatus, and an ink tank is freely attachable to and detachable from said apparatus; a type in which an ink tank is constituted integrally with a recording head, and the resultant integrated unit is freely attachable to and detachable from a carriage; and the like types.
In the former type of the tank, an ink is supplied to the recording head by providing a water head difference therebetween, while in the latter type, an ink is supplied to the recording head by providing the ink tank with a negative pressure generation source.
There have frequently been proposed in recent years, the ink-jet recording apparatuses which adopt the latter type of the ink tank from the viewpoints of miniaturizing the apparatus as well as the easiness of maintenance work.
Such an ink tank is required to be capable of favorably supplying an ink in an amount corresponding to the amount of the ink discharged from the recording head at the time of recording, and also to be tree from the leakage of an ink through a discharge port at the time of non-recording.
There is available for example, as an ink tank meeting the above-mentioned requirements, an ink tank in the form of cartridge in which a recording head is integrated with an ink tank, and an absorbent (foam) is filled inside the ink tank. It is made possible by such absorbent filled in an ink tank to maintain the ink meniscus at an stable level at the ink discharge portion of the recording head, and at the same time it is made possible by the capillary power of the absorbent to properly preserve the ink in the ink tank. In this case, it is needed that almost entire inside of the ink tank be filled in with the absorbent. Thus by allowing the absorbent to preserve an amount of ink a slightly less than the maximum preservable amount thereof, the capillary power of the absorbent is utilized to generate a negative internal pressure. It is therefore, made possible to minimize the amount of the ink leaking through the discharge portion of the recording head and through the ink tank portion communicating with the atmosphere, even in the case where a mechanical shock such as vibration or a thermal shock such as temperature variation is applied to the recording head or the ink tank.
The aforesaid method in which the ink tank inside is almost entirely filled with an absorbent involves the problems that the negative pressure of the absorbent increases accompanying the consumption of the ink, and increases the amount of the ink remaining in the ink tank without being supplied to the recording head, thereby bringing about a low utilization efficiency of the ink.
In order to solve such problems, there is proposed for example a cartridge for an ink-jet recording head which cartridge is constituted so that an ink reservoir is separated from a cavity by a wall equipped with a communication opening on the lower side of an ink tank, and an umbrella check valve is installed movably in the communication opening so as to discharge the ink in the ink reservoir into the cavity by opening itself at the point of time when the ink pressure in the ink-jet recording head is lowered, whereby the ink is supplied to the ink-jet recording head [refer to Japanese Patent Application Laid-Open No. 231759/1987 (Sho-62)].
According to the above-mentioned constitution it is made unnecessary to accomodate an absorbent in the cartridge, thereby enabling to enlarge the substantial accomodation capacity of the ink tank. In general, however, a serious problem with the aforesaid constitution remains unsolved in that the umbrella check valve has an offset value which is too high to precisely regulate the amount of the ink to be supplied to the recording head, thus bringing about unfavorable variation in the amount of the ink to be supplied and consequent deterioration of the quality of the printed letters.
There are also problems in the state of the umbrella check valve being opened, that the recording head is completely isolated from the ink reservoir, which increases the pressure in the cavity, destroys the seal at the connection to the recording head, and thereby causes ink leakage when the ink in the cavity is volumetrically expanded by 2 to 5%, approx. owing to the variation in the environmental temperature; and that in the state of the ink tank being mounted on the recording head, the increased pressure as mentioned above is applied as such to the recording head, which makes it impossibe to maintain a negative pressure between the recording head and the ink tank, and thereby causes ink leakage through the recording head.
There is further a problem that since the umbrella check valve is not imparted with a sufficient valve-opening power by several tens millimeter of water columnn that is to be maintained for the purpose of stably supplying the recording head with the ink, there is a fear that the valve is opened in response to the swing of the ink caused by the movement of a carriage, thereby bringing about inferior stability of the printed letters.
In order to solve the foregoing problems involved in such an umbrella check valve in such circumstances, an attempt is made for example to employ an ink tank valve which is installed at the position dividing an ink chamber and an ink supply portion, is moved by the difference in pressure between the ink chamber and the ink supply portion, and supplies the recording head with the ink filled in the ink chamber [refer to Japanese Patent Application Laid-Open No. 174860/1996(Hei-8)].
By equipping the ink tank with such an ink tank valve, it is made possible to certainly supply the recording head with the ink, by surely responding to the slight difference in pressure between the ink tank and the recording head without being influenced by the swing of the ink due to the movement of the carriage, while maintaining the negative pressure well suited for printing between the recording head and a recording medium. It is further made possible thereby to prevent the ink from leaking by variation in temperature through the ink supply port or through the recording head.
There is usually used in the ink tank valve, an elastic material, for example a plastic base-material to which an elastic material is adhesively bonded. As an elastic material, heat curable rubber has heretofore been used in general. However, there have been problems with the above-mentioned heat curable rubber, that it is difficult to carry out injection molding by means of two-color molding method along with a plastic; that the manufacture of the ink tank valve is expensive; and further that it is difficult to mold and vulcanize the material reduced in hardness into a member having a desired shape and form.
On the other hand, an ink tank for replacement has heretofore been equipped with an elastic member in the form of foam such as polyurethane foam at an ink supply port thereof in order to prevent the ink from leaking therefrom. The elastic member, however, sometimes fails to preserve the ink by preventing the ink leakage during a long period of service. Such being the case, an elastic member excellent in durability has eagerly been sought.
In the case where a recording apparatus is in a non-operational state in an ink-jet recording apparatus, a recording head is allowed to stand by at the end of the main body of the ink-jet recording apparatus. In order to prevent an ink from leaking through the recording head in such standing by, the recording head is accomodated on a sealing member which is arranged along a concave provided on the aforesaid main body of the ink-jet recording apparatus. A heat curable rubber, which is usually used for the sealing member, involves the problem same as the foregoing.